Exhaust gas purification catalyst on which influence of iron compound has been suppressed

ABSTRACT

An exhaust gas purification catalyst is provided which contains titanium oxide as a main component and an oxide of one element or two or more elements selected from the group consisting of tungsten (W), molybdenum (Mo), and vanadium (V) as an active component, wherein the exhaust gas purification catalyst contains phosphoric acid or a water soluble phosphoric acid compound so that the atomic ratio of phosphorus (P) to a catalytically active component represented by the following formula is more than 0 and 1.0 or less; 
     P/catalytically active component (atomic ratio)=number of moles of P/(number of moles of W+number of moles of Mo+number of moles of V).

TECHNICAL FIELD

The present invention relates to an exhaust gas purification catalyst,and more particularly to, a catalyst used for oxidizing elementalmercury (Hg) as well as reducing nitrogen oxides (NOx) contained in coalcombustion exhaust gas by ammonia, which can maintain to a very lowlevel an activity of oxidizing SO₂ contained in the exhaust gas to SO₃for a long period of time by suppressing an increase in the activity ofoxidizing SO₂ with the lapse of time by an increase in Fe compound, anda method of producing the same.

BACKGROUND ART

As the denitration catalyst for ammonia catalytic reduction, containingtitanium oxide as a main component has high activity and favorabledurability, it is generally used worldwide for the treatment of exhaustgas such as gas released from a boiler and constitutes the mainstreamdenitration catalyst (Patent Document 1).

In recent years, there is a rapid increase in demand for energy andcoals having high sulfur content (i.e., high S coals) start to be usedas fuel. In addition to this, a trouble caused by SO₃ increases, forexample, part of SO₂ is oxidized to SO₃ due to a SO₂ oxidizing activityof a denitration catalyst so that visible stack plumes originating fromSO₃ is released from a stack or a downstream equipment in a denitrationapparatus is corroded, etc. As such, in accordance with increased needsfor a denitration catalyst having very low SO₂ oxidizing activity, acatalyst with modified composition (Patent Document 2) and a catalysthaving a distribution in concentration of the catalyst components(Patent Document 3) are known.

Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No.50-128681

Patent Document 2: JP-A No. 2-184342

Patent Document 3: JP-A No. 09-220468

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Meanwhile, with regard to the SO₂ oxidation active site of a denitrationcatalyst, there are SO₂ oxidation active site that is intrinsic to thecatalyst component and SO₂ oxidation active site that is newly formed byadhesion of a Fe component contained in combustion ash to the catalystor by migration of a Fe component accompanied with corrosion of asubstrate to the catalyst, when a metal substrate is used for thecatalyst. In particular, due to the latter, a dramatic increase in SO₂oxidizing activity is caused when the degree of forming SO₂ active sitein the catalyst is huge. In particular, since Fe₂O₃ is contained at highconcentration of 20 to 30% by weight in combustion ash of high S coalsthat are produced in the United States, etc., for the treatment ofcombustion exhaust gas of such high S coals, it is necessary to suppressan increase in SO₂ oxidizing activity caused by adhesion of Fe₂O₃ to thecatalyst.

According to the conventional technology above described, SO₂ oxidationrate of the catalyst component itself can be suppressed to a low level,and therefore sufficiently low initial SO₂ oxidation rate is obtainedfor the catalyst. However, sufficient consideration regarding thesuppression of an increase in SO₂ oxidation rate of the catalyst that iscaused by an increase in a Fe component in the latter case was not made,and therefore the SO₂ oxidation rate of the catalyst with the lapse oftime is still big and improvements are needed in several aspects.

An object of the present invention is to provide, considering theproblems of the conventional technology above, an exhaust gaspurification catalyst that can suppress an increase in SO₂ oxidationwith an increase in a Fe component in the denitration catalyst with thelapse of time attributable to internal and external causes and, even inexhaust gases of fuels having a high Fe content such as high S coals,can realize operation at a low SO₂ oxidation rate for a long period oftime, and a method of producing the same.

MEANS FOR SOLVING THE PROBLEMS

Inventions that are claimed in the present application to achieve theobject described above are as follows.

(1) An exhaust gas purification catalyst containing titanium oxide as amain component and an oxide of one element or two or more elementsselected from the group consisting of tungsten (W), molybdenum (Mo), andvanadium (V) as an active component, in which the catalyst containsphosphoric acid or a water soluble phosphoric acid compound so that theatomic ratio of phosphorus (P) to a catalytically active componentrepresented by the following formula is more than 0 and 1.0 or less;

P/catalytically active component (atomic ratio) =number of moles ofP/(number of moles of W+number of moles of Mo+number of moles of V).

(2) An exhaust gas purification catalyst, wherein the catalyst describedin (1) above is supported on a metal substrate.

(3) A method of purifying exhaust gas, wherein the catalyst described in(1) or (2) above is used for purification of exhaust gas includingnitrogen oxide and ashes containing a Fe component.

(4) A method of producing an exhaust gas purification catalyst,including: adding an oxide or an oxo-acid salt of one element or two ormore elements selected from the group consisting of tungsten (W),molybdenum (Mo), and vanadium (V) to titanium oxide; adding water; andkneading followed by drying and calcination, wherein phosphoric acid ora water soluble phosphoric acid compound is added to the oxide or theoxo-acid salt thereof for a reaction so that the atomic ratio of P to acatalytically active component represented by the following formula ismore than 0 and 1.0 or less;

P/catalytically active component (atomic ratio)=number of moles ofP/(number of moles of W+number of moles of Mo+number of moles of V).

(5) A method of producing an exhaust gas purification catalyst,including: adding an oxide or an oxo-acid salt of one element or two ormore elements selected from the group consisting of tungsten (W),molybdenum (Mo), and vanadium (V) to titanium oxide; adding water;kneading followed by drying and calcination; and immersing the resultantin a solution that is prepared separately in advance by addingphosphoric acid or a water soluble phosphoric acid compound to an oxideor an oxo-acid salt of one element or two or more elements selected fromthe group consisting of tungsten (W), molybdenum (Mo), and vanadium (V)to be reacted so that the atomic ratio of P to a catalytically activecomponent represented by the following formula is more than 0 and 1.0 orless;

P/catalytically active component (atomic ratio)=number of moles ofP/(number of moles of W+number of moles of Mo+number of moles of V).

EFFECTS OF THE INVENTION

According to the invention, by having the atomic ratio of P to acatalytically active component in the catalyst to be within the rangedescribed above, formation of SO₂ oxidation active site in the catalystthat is caused by the adhesion of a Fe component comprised in ash fromgas to be treated is suppressed, and therefore SO₂ oxidation rate can bemaintained at a low level for a long period of time. In particular, fora catalyst using a metal substrate, formation of SO₂ active site causedby corrosion product containing a Fe component, that is generated whenthe catalyst is used in harsh condition, is prevented so that even forthe catalyst using a metal substrate as a carrier the SO₂ oxidation ratecan be maintained at a low level for a long period of time.

As the catalyst of the invention has not only high denitratingperformance and Hg oxidizing performance but also low SO₂ oxidationrate, when it is used for denitration of exhaust gas from a high S coalboiler used in the United States, etc., generation of SO₃ can besuppressed to a low level. Furthermore, since it is difficult for SO₂oxidation rate to increase even when the Fe component contained in ashor the like migrates into the catalyst, problems such as generation ofpurple smoke due to SO₃ resulting from oxidation of SO₂ can be avoidedwhen it is applied for exhaust gas of high S coals containing a greatamount of a Fe component.

Inventors of the present invention intensively studied the increase inSO₂ oxidation rate of the catalyst caused by a Fe component. As aresult, it was found that the increase in SO₂ oxidation rate proceedsthrough the following steps (1) to (4).

(1) Fe component such as iron oxide or the like adheres on the surfaceof a catalyst or corrosion of a metal substrate occurs at the interfacebetween the metal substrate and the catalyst component, but no increasein SO₂ oxidation rate occurs during this step. (2) The Fe component inthe catalyst is sulphated by SOx present in exhaust gas. (3) Thesulphate is dissolved in water which is absorbed when operation of acombustion furnace is on hold, and as a result, it migrates as a Fe ionto the inside of the catalyst. (4) The migrated Fe ion is adsorbed ontotitanium oxide to form SO₂ oxidation active site.

The inventors of the present invention were curious about thepossibility of preventing efficiently an increase in SO₂ oxidation rateby blocking the formation of SO₂ oxidation active site during step (4)among the four steps described above. In this connection, as a meanstherefor, a phosphorus compound is included in the catalyst so that theFe component is reacted with the phosphorus compound to form aninsoluble iron phosphate, and as a result the increase in SO₂ oxidationrate is prevented.

According to the invention, part of the catalytically active componentis present as a complex resulting from a qualitative reaction withphosphoric acid/phosphoric acid compound, and it is believed that Fe ionand the complex of phosphoric acid and the active component undergo thereaction as follows.

Fe ion+P₂O₅-WO₃ complex→FePO₄+WO₃  (Formula 1)

Fe ion+P₂O₅-MoO₃ complex→FePO₄+MoO₃  (Formula 2)

Fe ion+P₂O₅-V₂O₅ complex→FePO₄+V₂O₅  (Formula 3)

With the reactions above, the Fe ion forms insoluble iron phosphate bywhich absorption onto TiO₂ is inhibited, and therefore an increase inSO₂ oxidation rate is prevented. Furthermore, according to theinvention, WO₃, MoO₃ and V₂O₅ are also formed as an active componentalong with the generation of FePO₄. As such, it is also expected toobtain the effect of maintaining the denitration activity or Hgoxidation activity at a high level.

BEST MODE FOR CARRYING OUT THE INVENTION

To obtain the catalyst of the invention, it is important to have theatomic ratio of P to a catalytically active component in the catalyst tobe more than 0 and 1.0 or less. As P reacts with the catalyticallyactive component to lower the denitration activity, there is a tendencythat denitration activity is reduced by excessive P. In order for thesuppression of an increase in SO₂ oxidation rate by adhesion of a Fecomponent and the denitration activity to be compatible with each other,it is preferable that the atomic ratio of P to a catalytically activecomponent is more than 0 and 0.5 or less.

As for a raw material used for preparation of the catalyst, any one ofthe oxides, salts or the like of the corresponding component may beused. However, considering that the P compound needs to react with a Mocompound or a W compound and a V compound, by using soluble salts of thecorresponding compound, for example, oxo acid or ammonium salts of thecorresponding element and mixing them with titanium oxide in thepresence of water, favorable results may be easily obtained. Phosphoricacid/phosphoric acid compound (i.e., P compound) may be directly addedduring the process of producing the catalyst as described above.Alternatively, a method in which a compound obtained by reacting inadvance phosphoric acid/P compound (i.e., complex) or a solutioncontaining the compound is added during a process of kneading rawmaterials for producing the catalyst, aside from the W, Mo, and Vcompounds that are added as an active component, or it is immersed afterproducing the catalyst or the like may be adopted. The latter method ispreferable in that the influence of P on catalytic activity can beeasily controlled. Examples of the water soluble phosphoric acidcompound include ammonium dihydrogen phosphate and diammonium hydrogenphosphate.

To perform the purification of exhaust gas containing nitric oxides andelementary mercury (i.e., metallic mercury) by using the catalyst of theinvention, a reducing agent like ammonia is injected and reacted bycontact with the catalyst according to the method known per se in theart.

EXAMPLES

Herein below, the present invention will be described in detail in viewof specific examples.

Example 1

Titanium oxide (specific surface area: 290 m²/g, manufactured byIshihara Sangyo K.K.) (900 g), ammonium molybdate (107 g), ammoniummetavanadate (28.3 g), 85% phosphoric acid (68.3 g), silica sol (tradename: OS SOL, manufactured by Nissan Chemical Industries, Ltd.) (404 g),and water (50 g) were placed in a kneader, and then kneaded for 60minutes. Thereafter, while silica-alumina ceramic fiber (manufactured byToshiba Fine Flex K.K.) (151 g) was gradually added to the mixture, themixture was kneaded for 30 minutes, to thereby yield a catalyst pastehaving a water content of 27% by weight. The paste obtained was appliedonto a base material (thickness: 0.7 mm) produced by subjecting a SUS430 stainless steel plate (thickness: 0.2 mm) to a metal-lathprocessing; the base material was sandwiched between two polyethylenesheets; and the thus-sandwiched base material was passed through a pairof pressure rollers so that the meshes of the metal lath base werefilled with the paste. The paste-filled base material was air-dried, andthen calcined at 500° C. for two hours, to thereby obtain a catalyst ofthe invention. Composition of the catalyst of this invention was foundto have a Ti/Mo/V (atomic proportions) of 93/5/2, and a P/(Mo+V) (atomicratio) of 0.5.

Example 2

The catalyst of the invention was obtained in the same manner as Example1, except that ammonium molybdate used in Example 1 was replaced by anequimolar amount of ammonium metatungstate, to thereby obtain a catalystof the invention. Composition of the catalyst of this invention wasfound to have a Ti/WN (atomic proportions) of 93/5/2, and a P/(Mo+V)(atomic ratio) of 0.5.

Comparative examples 1 and 2

The catalyst was prepared in the same manner as Example 1 and Example 2,except that no phosphoric acid was added.

Examples 3 to 7

Titanium oxide (specific surface area: 290 m²/g, manufactured byIshihara Sangyo K.K.) (900 g), ammonium molybdate (113 g), ammoniummetavanadate (105 g), 85% phosphoric acid (18 g (Example 3), 53 g(Example 4), 88 g (Example 5), 124 g (Example 6) and 177 g (Example 7))and silica sol (trade name: OS SOL, manufactured by Nissan ChemicalIndustries, Ltd.) (404 g) were placed in a kneader, and then kneaded for60 minutes. Thereafter, while silica-alumina ceramic fiber (manufacturedby Toshiba Fine Flex K.K.) (151 g) was gradually added to the mixture,the mixture was kneaded for 30 minutes, to thereby obtain a catalystpaste having a water content of 27% by weight. The obtained paste wasapplied onto a base material (thickness: 0.7 mm) produced by subjectinga SUS 430 stainless steel plate (thickness: 0.2 mm) to a metal-lathprocessing; the base material was sandwiched between two polyethylenesheets; and the thus-sandwiched base material was passed through a pairof pressure rollers so that the meshes provided in the metal lath basewere filled with the paste. The paste-filled base material wasair-dried, and then calcined at 500° C. for two hours, to thereby obtaina catalyst of the invention. Composition of the catalyst of thisinvention was found to have a Ti/MoN (atomic proportions) of 88/5/7 anda P/(Mo+V) (atomic ratio) of 0.1, 0.3, 0.5, 0.7 and 1.0 for Example 3 to7, respectively.

Comparative example 3

The catalyst was prepared in the same manner as Example 3, except thatno phosphoric acid/phosphoric acid compound was added.

Example 8

Titanium oxide (specific surface area: 290 m²/g, manufactured byIshihara Sangyo K.K.) (900 g), ammonium molybdate (113 g), ammoniummetavanadate (42.9 g), ammonium dihydrogen phosphate (110 g), silica sol(trade name: OS SOL, manufactured by Nissan Chemical Industries, Ltd.)(404 g) and water (50 g) were placed in a kneader, and then kneaded for60 minutes. Thereafter, while silica-alumina ceramic fiber (manufacturedby Toshiba Fine Flex K.K.) (151 g) was gradually added to the mixture,the mixture was kneaded for 30 minutes, to thereby obtain a catalystpaste having a water content of 27% by weight. The obtained paste wasapplied onto a base material (thickness: 0.7 mm) produced by subjectinga SUS 430 stainless steel plate (thickness: 0.2 mm) to a metal-lathprocessing; the base material was sandwiched between two polyethylenesheets; and the thus-sandwiched base material was passed through a pairof pressure rollers so that the meshes provided in the metal lath basewere filled with the paste. The paste-filled base material wasair-dried, and then calcined at 500° C. for two hours, to thereby obtaina catalyst of the invention. Composition of the catalyst of thisinvention was found to have a Ti/MoN (atomic proportions) of 93/5/3 anda P/(Mo+V) (atomic ratio) of 0.4.

Example 9

Titanium oxide (specific surface area: 290 m²/g, manufactured byIshihara Sangyo K.K.) (900 g), molybdenum trioxide (88 g), ammoniummetavanadate (42.9 g), ammonium dihydrogen phosphate (110 g), silica sol(trade name: OS SOL, manufactured by Nissan Chemical Industries, Ltd.)(404 g) and water (50 g) were placed in a kneader, and then kneaded for60 minutes. Thereafter, while silica-alumina ceramic fiber (manufacturedby Toshiba Fine Flex K.K.) (151 g) was gradually added to the mixture,the mixture was kneaded for 30 minutes, to thereby obtain a catalystpaste having a water content of 27%. The obtained paste was applied ontoa base material (thickness: 0.7 mm) produced by subjecting a SUS 430stainless steel plate (thickness: 0.2 mm) to a metal-lath processing;the base material was sandwiched between two polyethylene sheets; andthe thus-sandwiched base material was passed through a pair of pressurerollers so that the meshes provided in the metal lath base were filledwith the paste. The paste-filled base material was air-dried, and thencalcined at 500° C. for two hours, to thereby obtain a catalyst of theinvention. Composition of the catalyst of this invention was found tohave a Ti/MoN (atomic proportions) of 93/5/3 and a P/(Mo +V) (atomicratio) of 0.4.

Comparative examples 4 and 5

The catalyst was prepared in the same manner as Examples 8 and Examples9, except that no ammonium dihydrogen phosphate was added.

Example 10

Ammonium metavanadate (42.9 g) was dispersed in water (100 ml) and addedwith 85% phosphoric acid (45 g). According to the reaction between them,a red slurry-like product was obtained.

Separately from the above, titanium oxide (specific surface area: 290m²/g, manufactured by Ishihara Sangyo K.K.) (900 g), ammonium molybdate(117 g), ammonium metavanadate (103 g), and silica sol (trade name: OSSOL, manufactured by Nissan Chemical Industries, Ltd.) (404 g) wereplaced in a kneader, and then kneaded for 30 minutes to obtain a past.To the paste, the red slurry obtained from the above was added andkneaded further for 30 minutes. Thereafter, while silica-alumina ceramicfiber (manufactured by Toshiba Fine Flex K.K.) (151 g) was graduallyadded to the mixture, the mixture was kneaded for 30 minutes, to therebyobtain a catalyst paste having a water content of 27% by weight. Theobtained paste was applied onto a base material (thickness: 0.7 mm)produced by subjecting a SUS 430 stainless steel plate (thickness: 0.2mm) to a metal-lath processing; the base material was sandwiched betweentwo polyethylene sheets; and the thus-sandwiched base material waspassed through a pair of pressure rollers so that the meshes provided inthe metal lath base were filled with the paste, to thereby obtain acatalyst of the invention. Composition of the catalyst of this inventionwas found to have a Ti/Mo/V (atomic proportions) of 85/5/10 and aP/(Mo+V) (atomic ratio) of 0.2.

Example 11

Titanium oxide (specific surface area: 290 m²/g, manufactured byIshihara Sangyo K.K.) (900 g), ammonium metavanadate (105 g), and silicasol (trade name: OS SOL, manufactured by Chemical Industries, Ltd.) (404g) were placed in a kneader, and then kneaded for 60 minutes.Thereafter, while silica-alumina ceramic fiber (manufactured by ToshibaFine Flex K.K.) (151 g) was gradually added to the mixture, the mixturewas kneaded for 30 minutes, to thereby obtain a catalyst paste having awater content of 27% by weight. The obtained paste was applied onto abase material (thickness: 0.7 mm) produced by subjecting a SUS 430stainless steel plate (thickness: 0.2 mm) to a metal-lath processing;the base material was sandwiched between two polyethylene sheets; andthe thus-sandwiched base material was passed through a pair of pressurerollers so that the meshes provided in the metal lath base were filledwith the paste. The resulting catalyst was air-dried, and then calcinedat 500° C. for two hours, to thereby obtain a catalyst of the invention.

Separately from the above, ammonium molybdate (112 g) was dispersed inwater (200 ml) and added with 85% phosphoric acid (89 g) to obtain asolution in which the two components are reacted with each other. Tothis solution, the catalyst obtained from the above was immersed, theliquid was removed, and then the catalyst was air-dried at roomtemperature or calcined at 350° C. for one hour, to thereby obtain acatalyst of the invention. Composition of the catalyst of this inventionwas found to have a Ti/Mo/V (atomic proportions) of 88/5/7 and aP/(Mo+V) (atomic ratio) of 0.5.

Use example 1

Each of the catalysts prepared in Examples 1 to 11 and Comparativeexamples 1 to 5 was cut into test pieces, each having a rectangularshape with a size of 100 mm×20 mm. The test pieces of each catalyst werebrought into contact with the gas under the condition shown in Table 1to measure the denitrating performance and the Hg oxidation rate of thecatalyst. Furthermore, they were brought into contact with the gas underthe condition shown in Table 2 to measure the SO₂ oxidizing performanceof each catalyst, and the initial activity was also determined.

Meanwhile, combustion ash of bituminous coal known as high S coals(e.g., coal produced in the eastern United States, Fe₂O₃ content of 26%by weight) was pulverized with a ball mill until 200 mesh pass ratio isat least 95% to prepare simulated ash. This simulated ash was applied toa vat, added with the catalyst of Examples 1 to 11 and Comparativeexamples 1 to 5, and added further with the simulated ash to havethickness of about 1 mm. The vessel was placed in a calcination furnacein which atmosphere is adjusted to have SO₂ of 500 ppm, humidity of 10%and air for the remainder, and the vessel was kept at 400° C. for 50hours. After that, the vessel was kept for 100 hours under the conditionincluding the temperature of 35° C. and relative humidity of 100%.Accordingly, the Fe components included in the ash were forced to moveinto the catalyst. As a result of fluorescent X ray analysis, the Fe₂O₃concentration on the surface of the catalyst was increased about 2.6% byweight on average. The Fe₂O₃ was increased up to 0.38% by weight onaverage compared to the whole components of the catalyst.

In order to determine the increase in SO₂ oxidation rate caused byadhesion of the Fe component to the catalyst which is obtained after theFe migration test, SO₂ oxidation rate of each catalyst was measuredunder the condition described in Table 2. The test results and theinitial performance are summarized in Table 3.

From the results of Table 3, it is found that the catalyst of theinvention has higher denitration rate and Hg oxidation rate with muchlower SO₂ oxidation rate compared to the catalyst of the Comparativeexamples. In addition, according to the test in which the Fe componentsare forced to adhere, the SO₂ oxidation rate has dramatically increasedwith the catalyst of the Comparative examples, while the increase in theSO₂ oxidation rate was minor for the catalyst of the present invention.Thus, it is found that the catalyst of the invention is resistant to theadhesion of a Fe component.

TABLE 1 Item Value 1. Gas composition NOx 300 ppm NH₃ 300 ppm SO₂ 1000ppm O₂  3% CO₂ 12% H₂O 12% Hg 10 ng/liter HCl 30 ppm 2. Gas flow amount3 liter/minute 3. Temperature 350° C. 4. Catalyst charge 20 mm width ×100 mm (entire length) amount 3 pieces

TABLE 2 Item Value 1. Composition SO₂ 500 ppm O₂ 3% 2. Gas flow amount1.2 liter/minute 3. Temperature 380° C. 4. Catalyst charge 20 mm width ×100 mm (entire length) amount 3 pieces

TABLE 3 SO₂ oxidation rate (%) Denitration Hg oxidation After the FeCatalyst rate (%) rate (%) Initial stage Adhesion test Ex. 1 94 83 0.70.9 Ex. 2 94 81 0.6 0.7 Ex. 3 98 92 3.4 3.8 Ex. 4 97 85 1.8 2.1 Ex. 5 9783 1.9 1.9 Ex. 6 96 90 1.2 1.4 Ex. 7 94 86 0.9 1.1 Ex. 8 97 85 0.7 0.9Ex. 9 97 83 0.8 0.8 Ex. 10 97 85 1.7 1.9 Ex. 11 97 83 1.1 1.2 Comp. ex.1 97 91 2.7 4.3 Comp. ex. 2 97 89 2.8 3.9 Comp. ex. 3 98 86 23 21.0Comp. ex. 4 97 83 4.4 5.6 Comp. ex. 5 98 92 3.9 6.2

1. An exhaust gas purification catalyst containing titanium oxide as amain component and an oxide of one element or two or more elementsselected from the group consisting of tungsten (W), molybdenum (Mo), andvanadium (V) as an active component, wherein the catalyst containsphosphoric acid or a water soluble phosphoric acid compound so that theatomic ratio of phosphorus (P) to a catalytically active componentrepresented by the following formula is 0.2 to 1.0; P/catalyticallyactive component (atomic ratio)=number of moles of P/(number of moles ofW+number of moles of Mo+number of moles of V).
 2. An exhaust gaspurification catalyst, wherein the catalyst according to claim 1 issupported on a metal substrate.
 3. A method of purifying exhaust gas,wherein the catalyst according to claim 1 is used for purification ofexhaust gas including nitrogen oxide and ashes containing a Fecomponent.
 4. A method of producing an exhaust gas purificationcatalyst, comprising: adding an oxide or an oxo-acid salt of one elementor two or more elements selected from the group consisting of tungsten(W), molybdenum (Mo), and vanadium (V) to titanium oxide; adding water;and kneading followed by drying and calcination, wherein phosphoric acidor a water soluble phosphoric acid compound is added to the oxide or theoxo-acid salt for a reaction so that the atomic ratio of P to acatalytically active component represented by the following formula is0.2 to 1.0; P/catalytically active component (atomic ratio)=number ofmoles of P/(number of moles of W+number of moles of Mo+number of molesof V).
 5. A method of producing an exhaust gas purification catalyst,comprising: adding an oxide or an oxo-acid salt of one element or two ormore elements selected from the group consisting of tungsten (W),molybdenum (Mo), and vanadium (V) to titanium oxide; adding water;kneading followed by drying and calcination; and immersing the resultantin a solution that is prepared separately in advance by addingphosphoric acid or a water soluble phosphoric acid compound to an oxideor an oxo-acid salt of one element or two or more elements selected fromthe group consisting of tungsten (W), molybdenum (Mo), and vanadium (V)to be reacted so that the atomic ratio of P to a catalytically activecomponent represented by the following formula is 0.2 to 1.0;P/catalytically active component (atomic ratio)=number of moles ofP/(number of moles of W+number of moles of Mo+number of moles of V). 6.A method of purifying exhaust gas, wherein the catalyst according toclaim 2 is used for purification of exhaust gas including nitrogen oxideand ashes containing a Fe component.